In the 1990's the MAEs and Gigaswitches would give us an unscheduled failure of a major exchange point on a regular basis, which let us demostrate our disaster recovery capabilities. With the improved reliability, i.e. the PAIXes haven't had a catastrophic failure, we haven't had as many opportunities to demonstrate how well we can handle a disaster at those locations. Without creating an actual disaster, what if all the providers turned off their BGP sessions with other providers at a PAIX (or Equinix or LINX or where ever), both through the shared switch and private point-to-point links, for an hour. More than likely no one would notice, but then we would have some hard data. Individually providers have tested parts of their own network, but I haven't heard of any coordinated efforts to test recovery across all the service providers in a particular location.